In the midst of pondering on how to enhance the safety of lithium-ion batteries, and reduce the possibility of explosion caused by battery overheating, a large number of scientists must first resolve the challenging issue of “dendrites” that are formed during charge and discharge of batteries, for which University of California, San Diego (UCSD), has effectively prevented uncontrollable reactions through the concept of “spillway”.

Lithium-ion battery is widely praised for its fast charging speed, longer durability, and higher power density, compared to traditional battery technology. Mobile phones are small and portable thanks to the compact and powerful lithium-ion battery, though unfortunately, is far from being perfect. As charge and discharge frequency increases, the electrodes within the battery will start to form rigid branch-like lithium dendrites, which will eventually grow long enough to pierce through the separator that functions to reduce electric currents and heat, and result in short circuit inside the battery, thus diminishing its lifespan.

There are quite a number of solutions for suppressing lithium dendrites, including the use of electrolyte additives, multidimensional current collector, and surface modification of the separator, and yet they all possess issues such as complex procedures and unsatisfactory cycle life, for which scientists have proposed new countermeasures that include using ultrasound or special protective layers to prevent the growth of dendrites.

In this regard, the UCSD team has brought forward another solution, which is a minor adjustment on the battery’s separator. A lithium-ion battery is primarily formed with the electrolytes and separator between two electrodes, where ions will first depart from the lithium cathode (positive electrode), and pass through electrolytes and the separator, before arriving at the graphite anode (negative electrode).

Applying conductive carbon nanotubes onto the separator, the team managed to converge electrons, which were slowly released from the battery subsequently, on the carbon nanotubes, when dendrites formed and pierced through the separator. This method resembles the function of a “spillway”, which releases excessive water from the dam before the overflow of water leads to a dam failure.

Matthew Gonzalez, first author of the thesis, expressed that the new model of separator slowly discharges excessive electric charges, while also prevents electric charges being “overflown” to the side of cathode. The battery begins to discharge when lithium dendrites are intercepted, hence battery short circuit will not explode due to inadequate energy.

Testing shows that a lithium battery installed with a pristine separator would experience a slow and gradual deterioration process, where degeneration begins after 20 to 30 times of charging and discharging, whereas a battery with a traditional separator may experience sudden malfunction. The team expressed that there would not be any warnings ahead of battery explosion in the past, where a battery can catch on fire abruptly from functioning normally, with no predictability whatsoever, for which the problem has been eliminated with the installation of the new separator that emits advance warning.